The present invention relates to filtering screens, and particularly to well screens which filter particulate matter out of a fluid as it is drawn from a well. More particularly, the present invention relates to well screens used to filter sand out of oil or gas as it is being drawn from a well.
A typical oil or gas well includes a xe2x80x9cstringxe2x80x9d which extracts oil from the well. The string generally constitutes a tube which provides a pathway to the Earth""s surface for subterranean oil or gas. The string typically includes a plurality of casing or joint assemblies positioned along the string in the oil or gas bearing portions of the formation being drilled. A casing or joint assembly portion typically includes a perforated base pipe through which oil and gas can flow. In this way, oil or gas enters the string and is drawn to the Earth""s surface.
However, because oil and gas producing wells are often drilled through unconsolidated formations, such as sandstone, the oil or gas must be filtered before flowing through the perforated base pipe and entering the string. Therefore, the casing or joint assembly typically includes one or more screen segments covering the perforated base pipe, so particulate matter in the oil or gas will be removed from the fluid before it enters the string. The existence of sand in the fluid being produced (e.g., oil, gas, water, etc.) is undesirable because it causes extra wear and abrasion on production tubing, valves, pumps, and other equipment used to produce fluids from wells.
Thus, a typical casing or joint assembly includes a perforated base pipe with one or more screen segments wrapped around it. The perforated base pipe and screen assembly is in turn encased in an outer, perforated jacket which protects the screens from damage as the string is lowered into the formation.
Plugging or clogging of the screen or screens around the perforated base pipe can severely decrease the production of the well. In conventional casing or joint assemblies, if that portion of the well screen directly over a particular base pipe perforation becomes completely clogged, no further oil or gas can flow through that perforation and it is rendered useless. As portions of the screen above particular base pipe perforations become clogged, the number of base pipe perforations through which oil can flow is severely decreased and the production of the well correspondingly goes down. Moreover, as the screen becomes clogged, the flow rate through unclogged portions increases causing increased wear and tear on those portions.
A casing or joint assembly which maximizes the usefulness of every perforation in the base pipe, even when portions of the well screen are clogged, would be welcomed by those in the oil, gas and other fluid producing industries.
According to the present invention, an oil well casing includes a filtering medium separated from a perforated base pipe by a spacer. The spacer is positioned to lie between the perforated base pipe and the filtering medium to space the filtering medium from the base pipe. The spacer forms a channel or channels between the filtering medium and the perforated base pipe connecting multiple base pipe perforations. In this way, fluid passing through a given portion of the filtering medium is permitted to subsequently flow through an aperture in the perforated base pipe which is not necessarily aligned with that portion of the filtering medium through which the fluid has just passed. In other words, according to the present invention, if a portion of the filtering medium directly above a given base pipe perforation is clogged, the base pipe perforation is still useful because fluid flowing through other, unclogged, portions of the filtering medium may travel via the channel or channels to the perforation.
In preferred embodiments, the spacer includes a spirally-wrapped wire and the filtering medium includes a wire-mesh screen. Consecutive turns of the spirally-wrapped wire create a channel between the wire-mesh screen and the perforated base pipe. The channel may have a width approximately equal to the diameter of the perforations in the base pipe and provides a connection between the various perforations.
Additional features and advantages will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.